Underseat Subwoofer

[Rikku]

Hi!

This is my first time posting here, so greetings! I wish to connect a Pioneer TS-WX130DA underseat subwoofer to the stock head unit on my 2015 Aygo (touch screen model). Till now, I know that I have to connect a wire to the Battery for power, a ground wire, a remote power wire so it turns on with ignition and either 2 rca's or high speaker input.

I have figured out that I can connect the ignition wire to a blue wire which comes out of the harness from the head unit, so that should'nt be a problem.

Now my problem is, how can I determine which are the speaker wires from the harness that is connected to the headunit and the polarity, and how can I determine if the wires are going to the 2 front tweeters or the 2 bigger 6.5" Speakers inside the doors? I have been searching all around but found no concrete diagrams, but fortunately someone from a Facebook group mentioned that the wires should be green and grey, and that I should use a high to low converter and connect the sub via rca's to that as connecting directly might mess up the impedance of the system. Is he right in saying that the connections are green and grey? And also, would it be possible to instead get some sort of adapter without splicing anything? I found harnesses with 3 added wires, left channel audio, right channel audio and video, but im guessing those will not work with a sub as they require you to enter into AV mode to then view whatevers connected.

Any help would be appreciated immensely, as this is my first time and I don't want to ruin anything!

Thanks!